Preparation method of hollow grouting type anchor rod

Abstract

The invention discloses a preparation method of a hollow grouting type anchor rod. The technical problems that an existing hollow grouting type anchor rod prepared from a hot-rolled steel plate with the yield strength of 550 MPa is high in production cost, and the elongation after fracture of the anchor rod is low are mainly solved. According to the technical scheme, the preparation method of the hollow grouting type anchor rod comprises the steps that (1) a hot-rolled steel plate is subjected to splitting and roll forming; (2) an anchor rod blank is prepared, specifically, the rolled hot-rolled steel plate is made into a welded pipe through high-frequency induction welding, the welded pipe is cooled with water after welding is completed, the anchor rod blank is obtained, the power of high-frequency induction welding is 150-300 kVA, and the welding speed is 20-30 m / min; and (3) the anchor rod blank is subjected to induction heating, thread rolling and water cooling, and the finished anchor rod is obtained. The maximum bearing capacity of the finished anchor rod is larger than or equal to 180 kN, and the percentage elongation after fracture of the anchor rod is larger than or equal to 12%. The anchor rod is mainly used for keeping long-term supporting of tunnels, mines and the like under complex geological conditions.

Description

Technical Field

[0001] This invention relates to a method for preparing anchor bolts, and more particularly to a method for preparing hollow grouting anchor bolts. Specifically, it relates to a method for preparing hollow grouting anchor bolts using hot-rolled steel plates with a yield strength of 460 MPa, belonging to the field of steel material processing. Background Technology

[0002] Rock bolts are a fundamental component of roadway support in modern underground mining. Widely used in mine roadway support, they reinforce the surrounding rock, enhancing its strength and ensuring the safety of underground mining spaces. Now, rock bolts are not only used in mines but also in engineering projects for the main reinforcement of slopes, tunnels, and dams.

[0003] Before the commencement of anchoring projects, destructive pull-out tests are required to verify the performance of the designed anchor bolts. The purpose of these tests is to determine the ultimate bearing capacity and elongation after fracture of the anchor bolts, to verify their performance and safety under conditions exceeding the design tensile force and approaching the ultimate tensile force, and to promptly identify defects in the design and construction of the anchor bolts so that the structural parameters of the anchor bolts can be adjusted or the manufacturing process improved before their formal use.

[0004] The main process for manufacturing hollow grouting anchor bolts involves hot-rolled steel coils being slitted, roll-formed, and high-frequency welded into anchor bolt blanks. These blanks are then subjected to high-frequency induction heating, thread rolling, and cooling to finally produce the finished anchor bolts. Anchor bolts must possess not only sufficient strength but also good toughness to fulfill their safety support function. Current technology uses materials with a yield strength of 550 MPa to manufacture anchor bolts, which is not only costly but also results in insufficient elongation at break due to losses in elongation at break during processing, failing to meet on-site requirements. Therefore, anchor bolt manufacturing requires not only high-quality raw materials but also strict control over the manufacturing process to achieve both cost-effectiveness and safety.

[0005] Chinese patent application CN 208280937U discloses a reinforcing anchor for tunnel construction.

[0006] This utility model discloses a reinforced anchor bolt for tunnel construction, comprising: a rod body with an external thread at one end, multiple grout outlet holes spaced apart on the rod body, and multiple elastic attachments spaced apart on the rod body and not interfering with the grout outlet holes; a cone head disposed on the other end of the rod body and detachably connected to the rod body; a sleeve selectively fitted onto the rod body, wherein when the sleeve is fitted onto the rod body, the multiple elastic attachments are located inside the sleeve and close to the rod body, and part of the external thread is located inside the sleeve and the other part is located outside the sleeve; and a nut disposed on the external thread, wherein when the sleeve is fitted onto the rod body, the nut abuts against the end of the sleeve near the rod body. This utility model can increase the friction between the anchor bolt body and the rock mass, thereby increasing the anchoring force of the anchor bolt on the rock mass, and achieving the effect of efficient rock mass anchoring.

[0007] In existing technologies, the design of anchor bolts using alloying elements such as Nb, Ti, and V, based on the addition of a high content of Mn to steel, has the disadvantage of high alloy cost and elongation at break A < 21%, which cannot meet the requirement of elongation at break ≥ 12% after the anchor bolt is manufactured. Existing hollow grouting anchor bolts have high manufacturing costs and low elongation at break after the anchor bolt is manufactured. Summary of the Invention

[0008] The purpose of this invention is to provide a method for preparing hollow grouting anchor bolts, which mainly solves the technical problems of high production cost and low elongation after fracture of existing hollow grouting anchor bolts made of hot-rolled steel plates with a yield strength of 550MPa.

[0009] The technical concept of this invention is to use hot-rolled raw materials with slightly lower strength and higher elongation, and by setting the induction heating temperature range, the rolling speed and a suitable cooling scheme, the load-bearing capacity and elongation after fracture of the finished anchor bolts meet the requirements, thus achieving economical production.

[0010] The technical solution adopted in this invention is a method for preparing a hollow grouting anchor bolt, which includes the following steps:

[0011] 1) Hot-rolled steel sheets are slitting and roll forming; the chemical composition of the hot-rolled steel sheets by weight percentage is: C: 0.165%~0.2%, Si: 0.12%~0.22%, Mn: 0.55%~0.65%, P≤0.02%, S≤0.008%, Alt: 0.015%~0.035%, Ti: 0.045%~0.065%, with the balance being Fe and unavoidable impurity elements; the yield strength R of the hot-rolled steel sheets with a thickness of 3.0~6.0mm is... p0.2 The tensile strength is 460–610 MPa, and the tensile strength R is... m The strength is 550–720 MPa, and the elongation after fracture is A. 50 mm It ranges from 21% to 33%.

[0012] 2) Prepare anchor bolt blanks by using high-frequency induction welding to form welded pipes from hot-rolled steel plates after rolling. After welding, the welded pipes are cooled with water to obtain anchor bolt blanks. The power of the high-frequency induction welding is 150-300 kVA and the welding speed is 20-30 m / min.

[0013] 3) The anchor bolt blank is subjected to induction heating, thread rolling, and water cooling to obtain the finished anchor bolt; the induction heating temperature of the anchor bolt blank is 730~880℃, the thread rolling speed is 1.5~2.5m / min, and the cooling water flow rate of the anchor bolt blank after thread rolling is 10~20L / min.

[0014] Furthermore, during the preparation of the anchor bolt blank, the weld reinforcement on the front side of the welded pipe after water cooling is removed, while the weld reinforcement on the back side of the welded pipe is retained, which can improve the maximum bearing capacity of the finished anchor bolt.

[0015] The finished anchor bolts prepared by the method of the present invention have a maximum bearing capacity ≥180kN and an elongation at break ≥12%, which meets the requirements for use.

[0016] The hollow grouting anchor bolt of this invention is used for roadway support in tunnels and mines.

[0017] The rationale for the method of this invention is as follows:

[0018] 1. Setting the temperature of high-frequency induction heating

[0019] High-frequency induction heating utilizes the induced current generated in a conductor under the influence of a high-frequency magnetic field, as well as the heat generated by the conductor's own magnetic field. Experiments have shown that anchor bolts manufactured at high-frequency induction heating temperatures below 730℃ and above 880℃ have a maximum load-bearing capacity below 180kN, which does not meet field application requirements. Therefore, the high-frequency induction heating temperature range for hollow grouting anchor bolts made from hot-rolled plates of this strength grade is 730–880℃.

[0020] 2. Setting the thread rolling speed

[0021] Once the high-frequency induction heating temperature is set, the thread rolling speed directly determines the structure and properties of the anchor bolt. If the thread rolling speed is too low, the anchor bolt blank will be overheated, affecting the surface quality; if the thread rolling speed is too high, the load on the anchor bolt blank will increase during the thread rolling process. Therefore, the thread rolling speed set in this invention is 1.5–2.5 m / min.

[0022] 3. Cooling speed setting

[0023] After the anchor bolt blank undergoes thread rolling, the heated metal is rapidly cooled using water to achieve good mechanical properties in the finished anchor bolt. When the cooling water flow rate is less than 10 L / min, the rapid cooling effect on improving the material's load-bearing capacity cannot be achieved. When the cooling water flow rate is greater than 20 L / min, although ultra-rapid cooling is beneficial for improving the material's strength, excessively high strength will inevitably reduce the elongation after fracture. Considering the required performance of the anchor bolt, the cooling water flow rate is set at 10–20 L / min.

[0024] This invention utilizes hot-rolled steel plates with a yield strength of 460MPa, designed with medium carbon, low manganese, and high titanium. The hot-rolled steel plates are slit, rolled, and high-frequency welded. The resulting anchor bolt blanks are then heat-treated, thread-rolled, and cooled according to a specific process. The resulting anchor bolts meet the requirements for maximum load-bearing capacity and elongation after fracture. Compared to existing 550-strength grade materials, this invention achieves lower manufacturing costs and is easier to produce, making it particularly suitable for manufacturing hollow grouting anchor bolts for tunnels and mines.

[0025] Compared with existing technologies, this invention has the following advantages: 1. The method of this invention uses hot-rolled steel plates with a design yield strength of 460MPa (medium carbon, low manganese, and high titanium), resulting in anchor bolts with low production costs and excellent mechanical properties. Compared with existing 550 strength grade materials, it reduces the amount of alloy added, realizing the economical production of hollow grouting anchor bolts. 2. By controlling the induction heating temperature, thread rolling speed, and coordinating with a water cooling scheme, this invention enables the anchor bolt to have a maximum load-bearing capacity ≥180kN and an elongation at break of ≥12%. The resulting hollow grouting anchor bolt has the microstructure and properties to meet the requirements for field use, mainly in tunnels and mines, ensuring long-term support under complex geological conditions. Attached Figure Description

[0026] Appendix Figure 1 This is a metallographic image of the anchor bolt prepared in Example 1 of the present invention. Detailed Implementation

[0027] The present invention will be further described below with reference to Examples 1-5, as shown in Tables 1-3.

[0028] In embodiments 1 to 5 of this invention, the thickness of the hot-rolled steel plate is 3.5 mm.

[0029] Table 1 shows the chemical composition (by weight percentage) of the hot-rolled steel plate in the embodiments of the present invention, with the balance being Fe and unavoidable impurities.

[0030] Table 1. Chemical composition of hot-rolled steel plates according to embodiments of the present invention, unit: weight percentage

[0031]

[0032] Table 2 Mechanical properties of hot-rolled steel plates according to embodiments of the present invention

[0033]

[0034]

[0035] A method for preparing a hollow grouting anchor bolt, the method comprising the following steps:

[0036] 1) Slitting and roll forming of hot-rolled steel sheets;

[0037] 2) Prepare anchor bolt blanks by using high-frequency induction welding to form welded pipes from hot-rolled steel plates after rolling. After welding, cool the welded pipes with water, remove the weld reinforcement on the front side of the welded pipe, and retain the weld reinforcement on the back side of the welded pipe to obtain anchor bolt blanks. The power of the high-frequency induction welding is 150-300kVA and the welding speed is 20-30m / min.

[0038] 3) The anchor bolt blank is subjected to induction heating, thread rolling, and water cooling to obtain the finished anchor bolt; the induction heating temperature of the anchor bolt blank is 730~880℃, the thread rolling speed is 1.5~2.5m / min, and the cooling water flow rate of the anchor bolt blank after thread rolling is 10~20L / min.

[0039] Table 3. Manufacturing process parameters and performance indicators of anchor bolts in embodiments of the present invention.

[0040]

[0041] See Figure 1 The metallographic structure of the anchor bolt is ferrite with a small amount of pearlite, and the volume percentage of pearlite is less than 5%.

[0042] As shown in Table 3, the maximum bearing capacity of the finished anchor bolts in the embodiment is ≥180kN and the elongation after fracture is ≥12%, which meets the usage requirements.

[0043] In addition to the embodiments described above, the present invention may have other implementations. All technical solutions formed by equivalent substitution or equivalent transformation fall within the protection scope claimed by the present invention.

Claims

1. A method for preparing a hollow grouting anchor bolt, characterized in that, Includes the following steps: 1) Hot-rolled steel sheets are slitting and roll forming; the chemical composition of the hot-rolled steel sheets by weight percentage is: C: 0.165%~0.2%, Si: 0.12%~0.22%, Mn: 0.55%~0.65%, P≤0.02%, S≤0.008%, Alt: 0.015%~0.035%, Ti: 0.045%~0.065%, with the balance being Fe and unavoidable impurity elements; the yield strength R of the hot-rolled steel sheets with a thickness of 3.0~6.0mm is... p0.2 The tensile strength is 460–610 MPa, and the tensile strength R is... m The strength is 550–720 MPa, and the elongation after fracture is A. 50mm It ranges from 21% to 33%. 2) Prepare anchor bolt blanks by using high-frequency induction welding to form welded pipes from hot-rolled steel plates after rolling. After welding, the welded pipes are cooled with water to obtain anchor bolt blanks. The power of the high-frequency induction welding is 150-300 kVA and the welding speed is 20-30 m / min. 3) The anchor bolt blank is subjected to induction heating, thread rolling, and water cooling to obtain the finished anchor bolt; the induction heating temperature of the anchor bolt blank is 730~880℃, the thread rolling speed is 1.5~2.5m / min, and the cooling water flow rate of the anchor bolt blank after thread rolling is 10~20L / min.

2. The method for preparing a hollow grouting anchor bolt as described in claim 1, characterized in that, During the preparation of the anchor bolt blank, the weld reinforcement on the front side of the welded pipe after water cooling is removed, while the weld reinforcement on the back side of the welded pipe is retained.

3. The method for preparing a hollow grouting anchor bolt as described in claim 1, characterized in that, The maximum bearing capacity of the finished anchor bolt is ≥180kN, and the elongation after fracture is ≥12%.

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